Turbine device



F 1957 HIDEO sAGARA I TURBINE DEVICE 2 Sheets-Sheet 1 Filed Au 19, 1955 HS. l

Feb. 28, 1967 HIDEO SAGARA 3,306,577

TURBINE DEVICE Filed Aug. 19, 1965 2 Sheets-Sheet 2 FIG. 5

FIG. 7

United States Patent 3,306,577 TURBINE DEVICE Hideo Sagara, 530-19 S-chome Koogokita-machi,

Hiroshima-ski, Japan Filed Aug. 19, 1965, 'Ser. No. 481,008 Claims priority, application Japan, Aug. 25, 1964, 39/ 38,330; Aug. 27, 1964, 39/ 18,913 Claims. (Cl. 25377) The present invention relates to a turbine rotor around the outer periphery of which a plurality of turbine blades are fastened radially, and more specifically to a turbine rotor to be driven by steam, gas or the like.

The blades of a steam or gas turbine are subject to a great centrifugal force and thrust due to the action of the working fluid. The latter causes the blades to vibrate so that the blades must'be made of materials that can bear such vibration and the row of the blades must have a structure capable of withstanding resonant vibration. However, it is very expensive to construct a turbine rotor with a strong structure and made of a material having high heat resistance and of vibration-resistant characteristics.

Further it may be sometimes observe-d that due to the inevitable changes in loads occurring in the operation of a turbine rotor, the turbine rotor is subjected to extraordinary temperature distribution Which causes a change in the natural vibration of a turbine blade to a resonant condition due to the thrust of working fluid such as gas,

steam or the like and thus results in the breakdown of the blade. V

Bearing in mind the foregoing, an object of the present invention is to eliminate the above mentioned disadvantages in a simple Way.

Another object of the present invention is to provide a turbine rotor wherein the row of the blades fastened radially around the outer periphery of a turbine rotor is divided into a plurality of groups of turbine blades whose tip portions are interconnected integrally and wherein the groups which are contiguous to each other have different numbers of turbine blades.

A further object of the present invention is to provide a turbine rotor made of a material which will not require special high characteristics in vibration resistance and in damping of vibration.

A still another object of the present invention is to provide a turbine rotor wherein excessive stress will not be produced at projecting portions of the blade roots even when a small number of blades in the blade groups are formed by interconnecting the tip portions of the successive blades in one row.-

Therefore a still further object of the present invention is to provide a low cost turbine rotor the blades of which will not be damaged during operation.

The above and other objects and advantages of the present invention will be apparent in the course of the following description of embodiments thereof in connection with the accompanying drawings wherein;

FIG. 1 is a partial side view of an embodiment according to the invention,

FIG. 2 is an enlarged view of FIG. 1 with the side of the rotor body broken away to show how the blades are fastened into an annular groove provided on the outer periphery of the rotor body,

FIG. 3 is a partial sectional view of the rotor body of FIG. 1 taken along line IIIIII of FIG. 1,

FIG. 4 is a front view of the turbine blade of FIG. 1,

FIG. 5 is a section taken along the line V-V of FIG. 4,

FIG. 6 is a partial sectional view of another embodiment of the present invention showing the turbine blades fastened into the rotor body, and

FIG. 7 is a partial side view of a still further embodiment of the invention illustrating the turbine blades being fastened into the rotor body from the lateral side thereof.

Referring now more particularly to FIG. 1 to FIG. 5, the rotor body of a steam turbine is generally represented by 1. The turbine 1 is provided with an annular groove or recess 7 extending inwardly from the outer periphery of the rotor body. The groove 7 includes a wide inner portion and an outer portion of less width formed between side projections 7'. A turbine blade generally designated 2 and includes a foot or rootvportion 6 having a projection 6 at the extreme inner end of the root on each 1 side which engage at the bottom portion of the groove 7 of the rotor body and a stem 6 which fits between the projections 7' in the groove whereby loosening of the blades in relation to the rotor body 1 can be prevented. At the same time the roots 6 are successively fitted into the groove 7 so that each root 6 contacts the back of the root of the contiguous blade. A plurality of blades 2 are fastened radially around the outer periphery of the rotor body 1. The contact faces between the projections 6' of the blade root 6 and the projections 7 of the turbine rotor body 1 are provided with relief surfaces 6 inclined inwardly in the direction of the rotor body axis. Owing to such surfaces of relief 6 the upper surfaces of the projection 6 on the web side are prevented from contacting with the rotor body 1 directly below the projection 7. (The area of the surface of relief 6 may be reduced as required by practice.) A shroud 3 is joined to the tip portions of three turbine blades 2 by means of rivets 5 to form a group A. A shroud 4 interconnects a group of blades B. The blade groups A and B are alternately positioned around the whole circumference of the rotor body 1 within the annular groove 7 and the contiguous shrouds 3 and 4 are arranged in close abutting engagement of their end faces.

Because the numbers of turbine blades in the blade group A and in the blade group B are different, the modes and the natural vibrations of the two groups in a tangential or axial direction thereof are quite different from each other. As to the mode of a blade group, the detailed explanation is given, for example, on pages 181- 194 of Transactions of the ASME, January 1958. At the same time, because of the difiFerence in the positionsof the adjacent blade groups A and B in relation to the nozzle from which high temperature and high pressure steam jets, there exists a phase difference between the vibromotive forces which are given to the blade groups A and B by the steam so that the phase difference in vibration also exists between the blade groups A and B.

As is clear from the above description, the contiguou groups of blades are subjectto different vibrations so that the vibration of the end blade of each group of blades is interferred with and damped by the vibration of the end blade of the contiguous group of blades. Thus the resonance of the blades is positively prevented.

I Consequently, a turbine rotor of a very high strength can be provided at a lower cost because it is quite unnecessary to use material selected for vibration resistance-and periodic damping characteristics or to design a blade of a considerable dimension in order to limit its vibration.

With the inventive construction the tendency for the blade root 6 to become loosened in the groove 7 because of the action of centrifugal force in high speed operation of the turbine rotor and because of difference in thermal expansion is lessened and thus the blade 2 is not apt to be deflected backwardly by thrust of steam. With the inventive construction the bending moment acting upon the blade 2 is received by the upper surface M of the backside of the blade root 6 and the lower surface N of the web side thereof, but the upper portion of the web side of the projection 6' is not subjected to the pressure force from the projection 7 because of the provision of the surface of relief 6 Consequently the corners 6 on the web side of the stem 6" of the blade root will not be subjected to great stress because of the surfaces of relief 6 but will only be subject to stresses due to a centrifugal force and a bending moment. Therefore cracks at the corner portions 6 can be prevented easily. Each turbine blade has a sufiicient strength to bear impact due to partial admission of steam even when a smaller member of the blades are interconnected to form a blade group.

In the embodiment of the invention just described above, the numbers of the blade groups A and B are three and four, respectively, but the group of blades B may be replaced with a blade group consisting of a set of two blades the tip portions of which are interconnected by one shroud. This can be accomplished because the mode and frequency of a blade group consisting of a set of two blades are different from those of the blade group A. In this case, when the group of blades consisting of a set of two blades is deemed to be too weak to bear the bending moment produced by jet stream, the factor of safety can be increased by very close contact of the tip portion of the backward blade of the blade group con- .sisting of the two blades with the tip portion of the forward blade of the contiguous blade. This provides a strength that corresponds to that of a blade group consisting of five blades.

In fastening the blades into the rotor body, when the alternate arrangement of the blade groups of different number of blades cannot be made for reasons of the total number of turbine blades and the positions of stopper blades, etc., two groups of blades consisting of the same number of blades must be disposed contiguously to each other at one location. However, because of the fact that the other ends of these contiguous groups are contiguous to the adjacent next blade groups consisting of a different number of blades, their respective vibrations are interfered with and damped at their contact points so that the amplitudes of the blade groups can be prevented from being increased to an excessive extent.

When the total number of blades in one row fastened radially around the outer periphery of the turbine rotor is about one hundred or so, the numbers of blades which are interconnected to form respective blade groups, which are alternately disposed, may be four and six. When the total number of blades in one row is about one hundred and fifty, the numbers of blades in respective blade groups may be determined to be six and eight respectively.

Further, the structure of a turbine rotor described above may be applied to a gas turbine and not only in the first stage but also in the successive stage. In accordance with the invention a turbine blade can be produced, without being limited strictly by a calculated natural vibration, whereby the efiiciency of aturbine is increased and at the same time the dimension of a turbine rotor is reduced, resulting in decrease of the cost thereof.

FIG. 6 illustrates another embodiment of the invention and parts therein equivalent to those in the first embodiment are designated by the same reference numerals. In this embodiment the rotor 1 is provided with a projection 7' and the blade is provided with a recess 6' for engagement on the projection.

FIG. 7 shows a still another embodiment of the invention and parts therein equivalent to those in the first embodiment are designated by the same reference numerals. However, in this embodiment around the outer periphery of a rotor shown in FIG. 7 are provided a plurality of projections 7 each having a Xmas tree-like contour and between them the roots 6 of the blades 2 are inserted from a lateral side of the rotor body 1 thereby to fasten blades 2 radially.

In the third embodiment the blade groups interconnected by means of shrouds 3 and 4 in the circumferential direction of the rotor body 1 have alternately different numbers of turbine blades, for example, three blades, four blades or two blades. Therefore, there exists a great difference in mode and frequency of vibration between the blade groups and the blades 2, 2 which are located at the ends of the adjacent blade groups. The abutting of the groups causes interference of such modes and frequencies directly or through the projections 7 on the rotor body so that the resonance of each blade can be prevented or suppressed. Furthermore, because of the fact that the surface of relief 6 is provided at the uppermost portion of the web side of the projection 6' of the blade root which engages with the projection 7' of the turbine rotor even when the blade 2 may be deflected backwardly by the thrust of working fluid, the bending moment acting upon the blade is received by the upper surface M of the backside of the blade root and the lower surface N on the web side of the blade root, so that in this case on the upper portion of the web side of the blade root no great stress is produced, whereby a sufficient strength is given to the turbine blade, as in the first mentioned embodiment of this invention.

What is claimed:

1. A turbine comprising a rotor having a recess defined around the periphery thereof, a plurality of turbine blades secured to the periphery of said rotor, each of said blades including a root portion engaged within the recess of said rotor, and shroud means interconnecting a plurality of said blades into a plurality of groups of blades extending around the periphery of said rotor, adjacent groups being of a different number of blades.

2. A turbine comprising a rotor having a recess do fined around the periphery thereof, a plurality of turbine blades secured to the periphery of said rotor, each of said blades including a root portion with a widened end engaged within the recess of said rotor, said widened ends of said blades having a relieved surface formed by an area of smaller dimension as a continuation of a sur face which bears radially outwardly against said rotor, and shroud means interconnecting a plurality of said blades into a plurality of groups of blades extending around the periphery of said rotor, adjacent groups being of a dif' ferent number of blades.

3. A turbine comprising a rotor having a recess defined around the periphery thereof, a plurality of turbine blades secured to the periphery of said rotor, each of said blades including a root portion with a widened end engaged within the recess of said rotor, said widened ends of said blades having a relieved undercut surface and a continuation surface which bears radially outwardly in respect to the rotor, and a peripheral shroud interconnecting the tips of a plurality of said blades into a plurality of groups of blades extending around the periphery of said rotor, said groups being in abutting relationship and the root portions of said blades being arranged in abutting relationship, at least some of said groups containing a different number of blades than the others of said groups.

4. A turbine comprising a rotor having a recess defined around its periphery extending radially inwardly and being widened at its inner end, a plurality of turbine blades having root portions with intermediate stems and widened inner ends arranged in the widened inner ends of said recesses, said widened inner ends being relieved at least along a portion of the area thereof at a location radially inwardly from its bearing engagement with said turbine rotor, a shroud interconnecting the outer tips of a plurality of said blades to form a first group of blades and interconnecting a plurality of tips of others of said blades to form a second group of blades, said first group having a different number of blades than said second group.

5. A turbine comprising a rotor having a recess defined around its periphery extending radially inwardly and being widened at its inner end, a plurality of turbine blades having root portions with widened inner ends arranged in the widened inner ends of said recesses, said widened inner ends being relieved at least along a portion of the area thereof at a location radially inwardly from its bearing engagement wit-h said turbine rotor, a shroud interconnecting the outer tips of a plurality of said blades to form a first group of blades and interconnecting a plurality of tips of others of said blades to form a second group of blades, said first and second groups being alternately arranged around the periphery of said rotor and being in abutting relationship, said first group having a different number of blades than said second group.

6. A turbine comprising a rotor having a substantially T-shaped recess defined around its periphery, a plurality of turbine blades having root portions with T-shaped ends engaged in the T-shaped recesses, said widened inner ends being relieved at least along a portion of the area thereof which is cut radially inwardly from its bearing engagement with said turbine rotor, a shroud interconnecting the outer tips of a plurality of said blades to form a first group of blades and interconnecting a plurality of tips of others of said blades to form a second group of blades, said first and second groups being alternately arranged around the periphery of said rotor and being in abutting relationship, said first group having a different number of blades than said second group.

7. A turbine comprising a rotor having a substantially T-shaped central projection extending around the periphery thereof, with a widened recess formed below each side of said T-shaped projection, a plurality of turbine blades having a substantially T-shaped recess positioned around said rotor blade with the recess engaged over the T-shaped projection, the blades having widened portions engaged in the widened portions of the recesses on said rotor, said blades having an undercut relief portion directly radially inwardly of each side of the T-shaped projection of said rotor, a shroud interconnecting the outer tips of a plurality of said blades to form a first group of blades and interconnecting a plurality of tips of others of said blades to form a second group of blades, said first and second groups being alternately arranged around the periphery of said rotor and being in abutting relationship, said first group having a different number of blades than said second group.

8. A turbine comprising a rotor having a recess defined around the periphery thereof, a plurality of turbine blades secured to the periphery of said rotor, each of said blades including a root portion engaged within the recess of said rotor, and shroud means interconnecting a plurality of said blades into a plurality of groups of blades extending around the periphery of said rotor including first and second groups, said first group being of a number which is 30 to of the number of the second group.

9. A turbine comprising a rotor having a recess defined around the periphery thereof, a plurality of turbine blades secured to the periphery of said rotor, each of said blades including a root portion engaged within the recess of said rotor, and shroud means interconnecting a plurality of said blades into a plurality of groups of blades extending around the periphery of said rotor, said groups being from 18 to 22 in number.

10. A turbine comprising a rotor having a recess defined around the periphery thereof, a plurality of turbine blades secured to the periphery of said rotor, each of said blades including a root portion with a widened end engaged with in the recess of said rotor, said widened ends of said blades having a relieved surface formed by an area of smaller dimension as a continuation of a surface which bears radially outwardly against said rotor, and shroud means interconnecting a plurality of said blades into a plurality of groups of blades extending around the periphery of said rotor, said relief surface being one sixth of the rotor bearing surface.

References Cited by the Examiner UNITED STATES PATENTS 1,959,220 5/1934 Robinson. 2,265,592 12/1941 Allen 25377 2,3 08,426 1/1943 Rettaliata 25 3-77 2,326,145 8/1943 Kroon 25377 2,414,278 1/ 1947 Soderberg. 2,431,249 11/1947 Heppner 253-77 X A FOREIGN PATENTS 1,281,536 12/1961 France.

890,803 9/1953 Germany.

MARTIN P. SCHWADRON, Primary Examiner.

EViERE'I'I E A. POWELL, JR., Examiner. 

1. A TURBINE COMPRISING A ROTOR HAVING A RECESS DEFINED AROUND THE PERIPHERY THEREOF, A PLURALITY OF TURBINE BLADES SECURED TO THE PERIPHERY OF SAID ROTOR, EACH OF SAID BLADES INCLUDING A ROOT PORTION ENGAGED WITHIN THE RECESS OF SAID ROTOR, AND SHROUD MEANS INTERCONNECTING A PLURALITY OF SAID BLADES INTO A PLURALITY OF GROUPS OF BLADES EXTENDING AROUND THE PERIPHERY OF SAID ROTOR, ADJACENT GROUPS BEING OF A DIFFERENT NUMBER OF BLADES. 